1. Field of the Invention
This invention is concerned with improving the flow properties and pour point characteristics of gas oils. Particularly, the invention is concerned with a fuel composition comprising a major amount of a gas oil and a minor amount of a high asphaltene residuum together with an effective pour depressant amount of, for example, an oil-soluble, high molecular weight ethylene-vinyl acetate copolymer or an oil-soluble block copolymer of the A--B--A type wherein the A block is an acrylate ester and the B block is a copolymer of ethylene and vinyl acetate. Another aspect of this invention relates to an improved pipeline transportation process for the above-described fuel compositions.
2. Description of the Prior Art
As is well known, many gas oils boiling at about 450.degree. to about 1050.degree. F. contain quantities of wax which render them viscous and give unacceptably high pour points. These oils behave as non-Newtonian liquids at low temperatures: exhibit variable solidifying temperature and peculiar hysteresis phenomena--all of which render them difficult to use as fuel.
One approach that could be used in converting these oils would be to subject them to fairly lengthy dewaxing procedures. This, however, would be an expensive procedure.
Another approach which has been used to bring the viscosity of the "crude" gas oils to suitable levels has been to dilute or "cut" them with a major amount of lighter distillate oils but this is an expensive procedure because of the considerably higher costs of the lighter distillate oils relative to the higher boiling oils. The distillate can be sold directly as a diesel fuel and as such is valuable and in short supply.
A number of additives have been suggested and tried with success in lubricating oils and in so-called middle distillates in order to tie in the wax therein and improve flow at low temperatures. Such additives consist either of compounds formed by alkylating benzene or naphthalene derivatives or of copolymers of ethylene-vinyl saturated aliphatic monocarboxylic acid esters of a molecular weight up to 3000 and containing from 15 to 25 percent by weight of the vinyl saturated aliphatic monocarboxylic acid ester. These additives are not, however, effective in depressing the pour point of certain fuel oil compositions.
In recent years the restrictive specifications limiting the sulfur content of fuel oils have made the manufacture of such fuels a much more difficult task than previously. In many localities, low-sulfur, high-pour fuels are being substituted for previously utilized high-sulfur, low-pour fuels. In order to meet the stringent pour point specifications of such fuel oils, pour depressants are being used. A particular effective class of pour depressants are, for example, the ethylene-vinyl acetate copolymers having molecular weights ranging from about 15,000 to about 60,000 and having and ethylene content of about 45 to about 90 percent. Although the ethylene-vinyl acetate copolymers have been shown to be effective in reducing the pour points of crudes and fuel oil blends containing distillate, they have not been found to be very effective in reducing the pour points of vacuum gas oils.
It is therefore the main object of the present invention to provide a fuel composition based on "crude" gas oils which will be free of the above-mentioned prior art limitations.
An equally important object of this invention is to provide a fuel oil composition having improved pour point characteristics by incorporating therein a minor amount of residuum and a small amount of certain highly effective pour depressants.